In conventional mass storage devices, such as disc drive data storage systems, media defect information is recorded in a defect table that is stored on the recording medium. In a disc drive, the defect table is typically stored in the reserved tracks of the recording medium. Conventionally the defect table has been of a fixed, predetermined sized, length and/or capacity.
The defect table indicates unreliable portions of the recording medium. During production of the mass storage device, the device is tested to determine which portions, if any, of the recording medium are not sufficiently reliable for writing and reading of a data. The address of each of the unreliable portions is stored on the recording medium in the defect table. When the mass storage device is running, the defect table is loaded into buffer random access memory (RAM), provided by a volatile memory device, that is also shared with interface transfer functions for the purpose of data caching.
Typically, larger defect tables for a mass storage device require more buffer (RAM) space. For a given quantity of RAM, this results in less buffer space being available for data caching. A typical disc drive type mass storage device with 80 gigabytes (GB) capacity would require not less than 64 kilobyte (KB) of buffer RAM to be reserved for defect table purposes. The size of the defect table is usually fixed across all disc drives of a particular type with different numbers of headers. A larger defect table size is usually required to insure that defects can be recorded, while at the same time meeting production yield requirements for the particular type of drive. Generally, production yield requirements include having a minimum number of storage devices fail due to insufficient defect table size.
For disc drive type mass storage device with more than 80 GB capacity, such as the 240 GB capacity drives, buffer RAM size the defect table may be as much as three times the buffer RAM size required for drives having less than 80 GB capacity. Thus, these drives may require that as much as 192 KB of buffer RAM be reserved for the defect table. This provides a significant impact to the performance of low-cost drives that use smaller sized buffer RAM. A method of reducing the portion of the buffer RAM occupied by the defect table, without increasing the number of mass storage devices that fail certification testing due to insufficient defect table storage capacity, would therefore be a significant improvement, particularly for low-cost disc drive type mass storage devices.
Embodiments of the present invention provide solutions to these and/or other problems, and offer other advantages over the prior art.